The present invention relates to a piston crank mechanism for reciprocating internal combustion engines having a crankshaft rotatable as a piston reciprocally moves. Specifically, the present invention relates to a multi-link piston crank mechanism in which a piston pin and a crank pin are connected with each other through a plurality of links.
Japanese Patent Application First Publication No. 2002-188455 (corresponding to U.S. Pat. No. 6,561,142) discloses a multi-link piston crank mechanism useable as a variable compression ratio mechanism for reciprocating internal combustion engines. The multi-link piston crank mechanism includes upper and lower links linking a piston pin of a piston to a crank pin of a crankshaft, and a control link linking the lower link to an engine block. The upper and lower links are connected with each other so as to be relatively pivotally moveable about a connection pin. The lower link is pivotally supported on the crank pin and connected to one end of the control link through a connection pin. The control link operates so as to restrain motion of the lower link. The control link has an opposed end swingably supported on the engine block, for instance, a lower portion of a cylinder block. The opposed end of the control link is coupled to a cam mechanism varying a position of the center of the swing motion of the opposed end. Owing to the operation of the cam mechanism, a top bottom center position of the piston and a compression ratio of the engine can be varied.
In view of lubricating performance in such a multi-link piston crank mechanism, it is preferred to use the connection pin of a full-floating type capable of connecting two links so as to permit relative pivotal motion thereof. In order to realize the full-floating connection construction of the connection pin, opposed end portions of the connection pin are projected outwardly from a pin boss of the link, and snap rings are mounted to snap ring grooves formed on the projected end portions of the connection pin. With the arrangement of the snap rings on the projected end portions of the connection pin, the connection pin can be prevented from removing from the link in the axial direction. The arrangement of the snap rings on the projected end portions of the connection pin is shown in FIG. 11 of the above-described related art.